LETTER TO THE EDITORS Obesity hypoventilation syndrome: prevalence and predictors in patients with obstructive sleep apnea

We agree with Dr. BaHammam that if clinicians only use a very high apnea–hypopnea index (AHI) as a predictor of obesity hypoventilation syndrome (OHS), it can lead to a significant underrecognition of this important syndrome. However, we have advocated using the serum bicarbonate as a first step because it is a highly sensitive test for detecting hypercapnia as it is physiologically related to the PaCO2. If clinicians are interested in not missing a the diagnosis of OHS, a condition that is associated with significant morbidity and mortality, then they should screen obese patients with obstructive sleep apnea (OSA) with a highly sensitive test (serum bicarbonate level) as a first step and not a highly specific test such as the AHI. In fact, our data demonstrated that in obese patients with OSA, a normal serum bicarbonate level practically ruled out OHS